Measuring long-range carrier diffusion across multiple grains in polycrystalline semiconductors by photoluminescence imaging

• Published in: Nature communications Vol. 4; no. 1; p. 2699
• Main Authors: Alberi, K., Fluegel, B., Moutinho, H., Dhere, R. G., Li, J. V., Mascarenhas, A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25-10-2013; Nature Publishing Group; Nature Pub. Group
• Subjects: 140/125; 639/301/119/1000; 639/301/930/2735; 639/766/25; Defects; Energy; Grain boundaries; Humanities and Social Sciences; Lasers; Measurement techniques; multidisciplinary; Science; Science (multidisciplinary); Semiconductors; Temperature
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3699

Thin-film polycrystalline semiconductors are currently at the forefront of inexpensive large-area solar cell and integrated circuit technologies because of their reduced processing and substrate selection constraints. Understanding the extent to which structural and electronic defects influence carrier transport in these materials is critical to controlling the optoelectronic properties, yet many measurement techniques are only capable of indirectly probing their effects. Here we apply a novel photoluminescence imaging technique to directly observe the low temperature diffusion of photocarriers through and across defect states in polycrystalline CdTe thin films. Our measurements show that an inhomogeneous distribution of localized defect states mediates long-range hole transport across multiple grain boundaries to locations exceeding 10 μm from the point of photogeneration. These results provide new insight into the key role deep trap states have in low temperature carrier transport in polycrystalline CdTe by revealing their propensity to act as networks for hopping conduction.
Understanding the role of defects on semiconductor carrier transport should help improve their performance in devices. Using photoluminescence techniques, Alberi
et al
. image the carrier diffusion in polycrystalline CdTe and find that long-range transport is mediated by the distribution of defect states.